Keep the promise small
The caption should explain what opens, such as an event sign-up page. Send the visitor to that page instead of a general homepage.
Use a stable tracking plan
If you need analytics, add campaign parameters to a URL you control or use your own redirect setup. A static graphic does not collect analytics by itself.
Check the final artwork
Test the exact poster or handout on different phones. Check that the destination loads quickly and that the form is usable on mobile.